The ongoing healthcare burden of seasonal Influenza, the emergence of strains resistant to existing treatments and the constant threat of new pandemic strains highlight the urgent need to identify new therapeutic targets against Influenza. The long term goal of our laboratory is to identify mechanisms of host defense against infection. The objective in this application is to identify host-encoded mechanisms of resistance to infection by Influenza. Based on emerging data and our preliminary studies, our central hypothesis is that the up-regulation of host 'restriction factors' that prevent viral entry restrict the ability of viruses to infect or replicate in host cells or increase the ability of cels to withstand viral-induced cytopathy represent an important strategy in host defense. Our rationale for the proposed work is that identification of such factors will provide a wealth of new targets fr therapeutic intervention, and that these may be less susceptible to resistance than viral-encoded targets. In the R21 phase we propose to use a novel unbiased forward-genetic approach to screen for host genes that confer resistance to Influenza infection. In the R33 phase, we will validate new host targets and use these insights to develop new anti-viral therapeutic strategies. Our screening approach is innovative because it allows identification of both host genes that, when overexpressed confer resistance ('restriction factors') as well as host genes required for infection, which are normally detected in conventional RNAi-based screens. The proposed work is significant because it has the potential to identify new targets, including non- coding RNA elements, which would be missed using existing approaches. Furthermore, our approach is responsive to the RFA because it is directed at identifying new host targets and therapeutic strategies to combat Influenza A and overcome resistance to existing antiviral agents.